Using a diffusion stone to carbonate is the most effective method. CO2 goes into solution very easily because the bubbles are so small and numerous. You can still use the higher pressure (make sure the stone is securely affixed or it may come off) but you can cut the time down to probably less than an hour. You won't need to shake the keg either to get the CO2 into solution. It's tough to force carbonate warmer than 50 *F. You will probably have to just about double the carbonation time from what it would be in the low 40s *F. Good luck
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